Credit: © 2006 ACS

Gold nanoparticles can be coated with short strands of DNA so that they can be linked together to form larger assemblies. To date, most research in this area has focused on uniform coatings, but now researchers in the US have shown that it is also possible to create coatings that make the nanoparticles asymmetric.

Chad Mirkin and co-workers1 at Northwestern University have used magnetic particles with diameters of 2.8 micrometres to template the formation of the asymmetric nanoparticles. The magnetic particles are coated with single strands of DNA, which are used to attach many smaller gold nanoparticles (13 nm in diameter) that are coated with complementary DNA sequences. The difference in size between the two types of particles means that a large number of gold nanoparticles surround each magnetic microparticle. Consequently, only a few of the DNA strands attached to the gold nanoparticles are bound to the larger particles. Moreover, only these strands are held in the correct position to be reacted with extension pieces of DNA that are also present on the template.

This means that the gold nanoparticles have an asymmetric DNA coating when they are released from the template. The localized area that was joined to the magnetic nanoparticle now has extended DNA strands, whereas the rest of the surface remains unmodified. Mirkin and co-workers go on to demonstrate that these asymmetric nanoparticles can assemble with directional control to give ‘cat paw’, satellite and dendritic structures.